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what do you think of these bricks?

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Marko

Sun Aug 13 2006, 11:40AM

Registered Member #89 Joined: Thu Feb 09 2006, 02:40PM
Location: Zadar, Croatia
Posts: 3145

Most-loved 'unregulated' SMPS is mazzili driver, just used with low-voltage secondary winding.

It offers a lot of power and voltage stability is pretty good with big loads (pulsed brick drivers aren't even considered a heavy load).

Reaching

Sun Aug 13 2006, 02:52PM

Registered Member #76 Joined: Thu Feb 09 2006, 10:04AM
Location: Hemer, Germany
Posts: 458

yeah, got it, bzw the small smps is ready to use and works fine. its just a simple flyback converter using a single irf630. outputs are 4x 15 volts 0,3A max 0,6A

heres a pic of the finished psu

i spend the whole day on it to make it work and i think i made my homework good

the psu already survived the longtime test with 4x 120mm fans as a load on all 4 outputs drawing 15volt 0,6A for 15 minutes, the mosfet only got warm ,not hot or so.

Marko

Sun Aug 13 2006, 03:28PM

Registered Member #89 Joined: Thu Feb 09 2006, 02:40PM
Location: Zadar, Croatia
Posts: 3145

Flyback converters without regulation sometimes do make trouble on high duty cycles.

The voltage spike that occurs will avalanche the mosfet unless it is dained by the load or some kind of clamping network.

Mosfet shouldn't get much more than room temperature with just few watts of load, and something is telling me that you are avalanching it.

Using resistor-diode clamping network and adequate snubber capacitor/network across mosfet could help him a lot staying cool.

You can also use a higher voltage mosfet sacrafycing a bit of ON resistance (altough I don't think it's really needed) to give more time for spike to drop.

Steve Ward

Sun Aug 13 2006, 06:17PM

Registered Member #146 Joined: Sun Feb 12 2006, 04:21AM
Location: Austin Tx
Posts: 1055

Eeep! i dont see any isolation between those windings on that flyback converter! I wouldnt trust that magnet wire to 900V or whatever.

Reaching

Sun Aug 13 2006, 06:27PM

Registered Member #76 Joined: Thu Feb 09 2006, 10:04AM
Location: Hemer, Germany
Posts: 458

ehm, 900volt?? those are 600volt igbts so i can only get up to rectified mains 309volts exactly and its double isolated magnet wire rated at 600volts, . or is there more voltage on the gate emitter than i expect, the potenzial should be no more than 30volts or so

on the other side, this powersupply only powers the gate driver ics on the driver boards, not the halfbridge, so there should be no voltage or isolation problem between those magnet wires.

for powering the halfbridges i dont think iÂ´ll use a smps, iÂ´ll use a normal transformer with 4 isolated windings. i dont know how much power the halfbridge draws on pulsed mode but i think its more than 1A or so, a smps with 200watt is difficult to build so iÂ´ll go with a normal transformer, better for a good dc voltage without any induced hf though ..

Hazmatt_(The Underdog)

Sun Aug 13 2006, 07:50PM

Registered Member #135 Joined: Sat Feb 11 2006, 12:06AM
Location: Anywhere is fine
Posts: 1735

What a pretty job you did Reaching. Nice PCB!

Steve Ward

Sun Aug 13 2006, 09:16PM

Registered Member #146 Joined: Sun Feb 12 2006, 04:21AM
Location: Austin Tx
Posts: 1055

Oops, i forgot this is going to be a 350VDC input system. Ok, well my point still stands. With voltage spikes, you will probably be up around 550V. The power supplies are isolated for a reason, they need to stand off this 550V. I guess if the magnet wire has not been damaged anywhere, it *might* be ok for this voltage... i still dont like it though. Many of the GDTs i made with magnet wire shorted out.

on the other side, this powersupply only powers the gate driver ics on the driver boards, not the halfbridge, so there should be no voltage or isolation problem between those magnet wires.

Each gate driver IC has its "ground" connection to the Source of the bottom fet in the half-bridge driver, which is referenced to the emitter of the main IGBT, whose voltage is swinging up and down 300++ volts. So even this power supply needs 4 isolated windings for each chip, and the isolation between the windings should be good for 600V id say.

i dont know how much power the halfbridge draws on pulsed mode but i think its more than 1A or so, a smps with 200watt is difficult to build so iÂ´ll go with a normal transformer, better for a good dc voltage without any induced hf though ..

My SMPS driving 4 drivers for a CM600 bridge is powered from a 12W transformer. It probably wouldnt handle CW use of course. But its fine at up to 10% duty cycle.

Reaching

Mon Aug 14 2006, 04:26AM

Registered Member #76 Joined: Thu Feb 09 2006, 10:04AM
Location: Hemer, Germany
Posts: 458

mhh, okay steve you made me careful, no problem iÂ´ll solve this "problem"

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